1. Field of the Invention
Exemplary embodiments of the present invention generally relate to an image forming apparatus and an image forming method performed by the image forming apparatus, and more particularly, to an image forming apparatus that forms a forcible toner consumption image on an image carrier when necessary to forcibly consume toner contained in developer contained in a developing unit, and an image forming method performed by the image forming apparatus.
2. Discussion of the Related Art
Related-art image forming apparatuses such as copiers, facsimile machines, and printers include a developing unit for containing developers used to develop a latent image formed on an image carrier such as a photoconductor into a toner image.
One known image forming apparatus employs a two-component developer that includes toner and magnetic carrier particles to convey the developer held on a developer carrier such as a developing roller to a development region located opposite the image carrier and transfer toner contained in the developer from a surface of the carrier onto the latent image formed on the image carrier, thereby developing the latent image into the toner image. The developer carrier conveys the magnetic carrier particles from the development region and returns them to the developing unit for reuse. The developers contained in the developing unit may be agitated while being supplied as appropriate, so that a toner concentration is maintained within a prescribed range.
However, if a known image forming apparatus having such developing unit frequently produces an image having a low image area, the developing unit may be run for a rather long period of time without consuming an appropriate amount of toner. As a result, the toner may be agitated excessively in the developing unit, which can degrade the toner. When the degraded toner is thus stressed, additives that are externally added to the surfaces of toner particles to adjust flowability and chargeability become separated from or embedded in the toner particles, thereby degrading the function thereof. Such degraded toners may contaminate a background part or non-image forming part on a surface of a recording medium, degrade development ability and transfer efficiency, etc., which can cause degradation of the quality of images such as contamination, degradation of image density, degradation of granularity, etc.
One approach to solving this problem is to provide an image forming apparatus that can calculate an output image area per unit of time based on an area of an output image. When a result of calculation is below a given threshold or when the toner contained in the developing unit is excessively agitated, the image forming apparatus forms a forcible toner consumption image to forcibly consume toner excessively agitated in the developing unit. When it is determined based on the area of the output image that the toner has been excessively agitated, the image forming apparatus may form the forcible toner consumption image to forcibly consume such toner.
However, in order to reduce costs, a known image forming apparatus adopting this approach is also designed to recycle the remaining toner. That is, after a toner image is transferred onto a recording medium or an intermediate transfer member, at least a small amount of residual toner remains on the surface of the image carrier. Such residual toner is then removed from the surface of the image carrier by a residual toner removal unit since, if the residual toner is discarded, unnecessary toner consumption may be conducted. Therefore, the remaining toner may be returned to the developing unit for recycling.
The above-described configuration, however, cannot sufficiently prevent accumulation of degraded toner particles in the developing unit because even though the toner particles excessively agitated in the developing unit are discharged from the developing unit by the formation of the forcible toner consumption image, the residual toner removal unit may still remove the forcible toner consumption image from the surface of the image carrier and returns the excessively agitated toner into the developing unit. Thus, the excessively agitated toner particles may continue to accumulate in the developing unit, defeating the purpose of employing the forcible toner consumption image in the first place.
Therefore, there is still a need for an image forming apparatus that can both effectively reduce the costs of toner usage by recycling residual toner remaining on the surface of the image carrier even after image transfer to a recording medium or an intermediate transfer member, as well as effectively suppress or prevent the quality of formed images from deteriorating due to accumulation of the degraded toner in the developing unit.